In the past, there has been provided an ultrasonic transducer such as an ultrasonic speaker (ultrasonic transmitter) producing an ultrasonic wave and an ultrasonic microphone (ultrasonic receiver) receiving an ultrasonic wave.
Further, in the past, there has been provided an ultrasonic sensor which detects an object by use of such an ultrasonic transducer. In other words, there has been proposed an ultrasonic sensor which transmits an ultrasonic wave and receives an ultrasonic wave reflected by an obstacle. For example, such an ultrasonic sensor includes a Doppler sensor configured to judge, based on a Doppler shift derived from a received ultrasonic wave, whether an obstacle is present.
As shown in FIG. 6, such an ultrasonic sensor is in use mounted on a bumper 1 of a vehicle (see document 1 [JP2010-194441 A]).
Such an ultrasonic sensor is described in detail below. The ultrasonic sensor shown in FIG. 6 is fixed to the bumper 1 by inserted into an exposing hole 11 formed in the bumper 1, and includes an outer block 41 inserted into the exposing hole 11 from an outside of the bumper 1 and an inner block 42 coupled to the outer block 41 in an inside of the bumper 1. In brief, the outer block 41 and the inner block 42 are coupled to each other such that the bumper 1 is interposed between the outer block 41 and the inner block 42. Hence, the aforementioned ultrasonic sensor is fixed to the bumper 1.
However, in such a structure in which the bumper 1 is interposed between the outer block 41 and the inner block 42 as shown in FIG. 6, part of the outer block 41 is protruded outside the bumper 1 (left side in FIG. 6). Thus, an appearance of the vehicle in which the ultrasonic sensor mounted on the bumper 1 is deteriorated.